The U.S. Census Bureau provides
2000 SF1 files with complete Summary File 1 files for the nation,
each state, the District of Columbia, and Puerto Rico.

Census also offers
American FactFinder (AFF) for looking up variables from 2000 Census SF1
and other Census data.

For example, to use AFF to find sex by age in the 2000 SF1,
click on
Decennial Census -> get data -> Topics -> Dataset -> 2000 SF1 100% Data ,
type 'sex by age' in the 'topic or table name' search box and click 'GO'.

The files below include all the 2000 SF1 data by 5 Digit ZIP Code Tabulation Area (ZCTA).
The files are split into 39 parts due to the large number of variables.